I have a 91 Jimmy and the the cable to the front diff only moves about an 8th of an inch, I am guessing this is why the 4x4 isn't working as all the others parts seem to be working fine. How far should the cable move in and out, and what might be damaged on the inside of the differential?
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4 wheel drive is unfortunately a bit of a myth as in 4 wd any two wheels with no traction will not move you any where
so if you have both rh side wheels slipping,
go no where
left front right rear ,
going no where
the wheel that was not turning was the only wheel that had traction but through the differential action the other wheel spun faster
now with limited slip diff centers , both wheels have to turn as the differential action locks up so yes you would be going some where.
posi traction is the same idea
vehicles that have limited slip diffs are Toyota and Nissan as standard with some Nissans having limited slip diffs in the front drive axle as well
now if you are doing a lot of 4wd driving in adverse conditions , you need to have locker diff centers ( available from off road shops ) as they physically lock the diff actions ( with the flick of a switch) with the result if all 4 wheels are spinning and you are not moving , your stuck but if one wheel has traction you keep moving
It is pretty close, but doing the math....
5th gear .814
diff gear 4.3
tire rpm = 1114
stock 91 tire size is 185/60-14
circumference = 71.31 inches
Completely stock, 3900 rpm gives you 75 mph. not the 70 you were claiming, but you could have smaller then stock tires (one inch less of diameter gives you 72 mph at 3900).
Hope this helps,
Check to see if the front diff is being engaged. Ther is a vac switch that come from the transfer case. It sits right on top has 3 lines. One line is vac input the other is vac output the third is a vent. When you push the 4wd button that switch allows the vac to the front diff. The front diff actuator is under the battery. Check to see if the actuator is moving if not check to see if the switch is any good by checking vac on the actutor line. You can doo this with out taking out the battery. You will see a line that goes from the back of the engine up the right side then under the batt. It is covered by wire loom. Cut in to it and see if there is vac. If not check to see the switch works. If there is then check to see if the actuator is torn( actuator looks like a cruse control actuator) or the cable to the front diff is stuck.
I have had the same problem with my Jimmy. While on a road trip in 2WD same as you, I slowed down for gas and same thing, nasty grinding. The problem is the collar that engages the front differential was grinding against the gear, eventually causing it to weld itself together. Putting the vehicle in 4WD takes the pressure off the fork which slides the collar over the gear. THE CAUSE OF THE PROBLEM is the air actuated switch on the transfer case, which is directly controlled by the switch on your dash. This switch gets hung up half way and causes the fork in the diff to move half way, which is where you get your grinding. Its incomplete meshing of the gears. The fork in the front diff is controlled by air from the air switch (or vacuum, lack of air, I cant remember) Take your jimmy to your local trans. and gear shop and have them check it out. The switch on the transfer case costed me $40 and replacing the bad gear and collar in the diff costed me $280. I did not have to rebuild the entire diff. Make sure you are not paying for parts you do not need. ask lots of questions!
Hope this didnt sound too complicated. By the way, I am also a fully certified truck transport mechanic.
Are you sure that your frame is not bent????? This will throw everything out of alliement. You will have to go from wheel to wheel and pull measurements like and X from side to side. fine the center point of the car and go from there. But it would be easer if you would put it on a frame machine!!!!!
Rich. There is a vacumn engagement of the front differential. The switch is on the transfer case. There will be a vacumn motor(looks like a curise control unit if you're familiar with them) under the hood with a cable running to the front diff. Make sure it functions when you engage 4wd. Probably does. If not, make sure it is getting vacumn by removing the line. It should **** on your finger when covered. If this all works properly, you could have trouble in the front diff. Don't forget the simple stuff, like CV joints, axle nuts tight, etc. You're driving an 86 so I assume you have a little experience in maintaince. Good luck. TJ
several places to check first one is the vac line on the ball mounted to your hood. if its ok then under the truck on the transfercase is the vac switch disconnect it and check for vac.. if you have it put vac line to actuator its uner the right innerfender it controls the front diff lock.. if its functioning then you just ned to replace the vac swithc in the transfercase its just screwed in.. the lines to the 4x4 system are plastic and rubber mostly..
sorry lost here ,never seen one but if transmission shaft is turning to front diff then the problem is their,could be anyting from a sheared diff pinion to a broken planet wheel or possible evan a snapped half shaft or the spline on the end of the half shaft has worn and rounded off